GrandmaAirplane

Did the same yesterday... cruising the CP to save a few bucks and booked one of those “Floating” cabanas (@$999 US).
YOLO rationale: We’re going to be 8 family members using it as our gathering place throughout the day... me, I won’t budge from it... the grandkids will love the slide & snorkel directly off the side... nice meal for lunch... we can cancel it later (if the reviews aren’t so great when they come in or the week before if the weather forecast is iffy)... there’s no way that price won’t increase and we couldn’t afford a higher price later (yeah, that one’s really silly - as we shouldn’t be spending that much now anyway ?) 

Interesting idea, Mr Candyman, thanks for ‘talking out loud’! ?

I'm talking out loud here but maybe it's possible for you to reach out to your Roll Call group to see if anyone (a party of 2) wants to share the cost of a Cabana with you so you can get their wristbands?  Based on the conversation, you only needed the wristbands for access so that your family can join you at your cabana. Plus you said there would only be 1-3 of you there at a time.  Offer them $10-$25 per wristband or whatever you think is fair.  They've already paid anyway so it's just money back for them.  You'll save them money and you wouldn't need to pay for a wasted cabana.

I will say that my husband slept on the sofa in our cabana,  it is fine to lie down on and take a nap.  It is deeper than you may think.  Hubby is 5'11 210 lbs.    They are firm, and plush.  I honestly can't remember if the back cushions were attached or not.  I just recall him sleeping on it, and I lifted his feet up so I could sit down, placed his feet on my lap while he was laying down.  My brother in law also slept on it during the day.  However, I will also say, this close to your sailing they maybe all sold out.   The bungalows also have a sofa, same style.  Bungalows only have 6 people, so you are still short 1 person since you have 7.
 Your other problem would be if your hubby wants shade to lay down in and you need the sofa.  Unlike the beach bed, the sofa does not take 2.  He would be left to sitting in 1 of the 2 chairs. I cannot answer that question.  My suggestion would be to call RCCL directly and explain your situation.  
 I know with our cabanas, which were pre-assigned like the beach beds, they assign by booking date/time.  IOWS, if you book 2 at the same time, they should be next to each other.  However, if you now add another bed, it may not be next to yours bc you booked yours way before you booked the 2nd one.  That being said, you are talking about a 30 second walk between the two beds.  
 

I believe the way they work children is the same as when you book a cabin.  If you had to pay for the child to sail, than yes, they count. If you are talking about the 5 and 8 yo than yes, they count, just like a bungalow or cabana.
The wristbands are not going to be transferrable.  They basically waterproof paper band with a glue type adhesive.  You will not be able to take it off and switch it to one person from another.
They will only give you 4 wristbands and that is it.  If I read tour post correctly, you actually would have 7 people total in your party.  There will be a concierge and they WILL STOP the 3 without wristbands from entering.    It is understandable why they do this, you maybe honest and just a 5 min. drop off, pop in and leave, but others may not be that honest.  All of the sudden where they had an 80 person max  (let's say 20 beds X 4), now bc they allow everyone to pop in, they could have 150 passengers in that area at any given time.  
The last time we did the beds (prior to Perfect Day) they did it the same way they did with us this time when we rented a cabana.
 They give you the directions to the concierge.  The principal passenger checks in and tells the concierge the other passengers that are allowed a wristlet.  You give their name and cabin number.  When that person shows up they tell them your name and they check them in and make sure they are on your list.  I know one time when I passed the cabana concierge there were 3 people saying that they just wanted to pop in to say hello to a specific person in a cabana.  They replied NO.  The concierge did say if you want I will walk over to their cabana and ask them to come over to the desk to say hello to you, but we can't allow you in.  My guess is that this will be true for you too.   When you ask about the snorkeling area are you asking where you get the gear, or where they actually swim to for snorkeling.  The snorkeling area is out there regardless whether you are in a lounger or the beds, basically that is due to how the beach area is designed.  If you have seen any pictures where you see the lifeguard platforms, it is still past that area.    
My suggestion is that you discuss with your family another meeting point.  For example, you stated they will be camping out by the pool.  The pool area is close to the grill for food.  So, although you have mobility issues, you might want to use that area as a staging area for you to pop over to see them.   The bathrooms are right next to Oasis lagoon, you can see the entrance to the pool area from the bathrooms, maybe a 2 min more walk to the lagoon pool.  Thus, if they get loungers closer to the entrance to the pool, by chill grill than it might be more doable for you.  
I am not sure what your mobility issues are, nor am I asking, but they do have beach wheelchairs, just realize somebody has to push.  I am not sure how you go about reserving one.  They are not like the ones on the ship, they have the big tires and are not electric.  They also have the trams and they run all day long, @ every 10 mins.  There are benches to sit on while you wait for the tram.  
Finally the only thing I can say from our last cruise where we did the cabana, the one thing I noticed was that by 3:00 the concierge attendants were non-existent.  All aboard for us was 5:15 (set sail was 6).  We left by 4:00 and passed the beach beds while riding the tram.  I would say 50%+ of the beach beds were already closed up (they cover the beds up for weather protection).  For our cabanas out of 20, maybe 4 still had people.   At every tram stop you saw the same thing, everything was emptying out really fast.  I think the main reasons why were simple:
 If you have early dining than you  are going to start packing up @ 3:30 so you can get back to the ship, change, take a shower and be ready for dinner  We docked early.  Our original debarkation time was 9.  They docked at 7:30, all of the crew was off the ship by 8.  They let us off by 8:30.  For most people 7 hrs was enough of sun and sand, so they started hauling out by 3:30  (we too were the only ship that day, Adventure of the Seas)  
 

@GrandmaAirplane
One last thing.  My hubby and I have done Coco Cay in early November.  It might have been the 2x we did it, but it was chilly in the a.m. when we got to the beach.  Maybe it is our age (early 50s), but we wore light weight cotton sweaters in the a.m.  I think we went into the water @10 bc we needed the air temp to rise, but even still when I did the walk into the ocean, he heard me say loudly "OH that is EXPLETIVE cold!    My hubby had no issue at all, but he is what I call a beach baby.  I was fine by 11 bc the air temp was now higher than the water temp.
FWIW I am a sissy when it comes to water temps.  I like bath water temps, which is why I love the Solarium pools!

The beds were pre-assigned.  When we got to our stateroom there was instructions and an assigned bed.  There is a map with it to show which beds are where.  Be sure to take the tram once you get off the pier, it will take you around to the check in concierge for the day beds.